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Maintenance of Pregnancy in Ovariectomized Heifers with Melengestrol Acetate

The Upjohn Company, Kalamazoo, Michigan

Abstract

Dairy heifers were bilaterally ovariectomized at about day 56 of pregnancy. Daily feeding of 4 mg. of melengestrol acetate (MGA) to heifers proved adequate to maintain pregnancy in seven of eight surviving heifers. A daily dose of 1 mg. maintained pregnancy for the first 30 days in 9 of 13 heifers, but pregnancy loss or fetal mummification occurred later in all but three of the heifers. Better results were obtained when the daily dose of MGA was begun 6 days prior to ovariectomy (seven of eight heifers) than on the day of ovariectomy (two of five heifers). In 11 heifers receiving 0.2 or 0.4 mg. daily, the loss of the pregnancy occurred shortly after ovariectomy. Beginning treatment with 4 mg. of MGA on day 4 resulted in establishment and maintenance of pregnancy in six of ten heifers. Withdrawal of MGA at day 270 in six heifers appeared to be associated with a higher incidence of retained placenta and in dystocia when compared with six heifers in which parturition occurred when 1 mg. of MGA was fed daily.

¹ Reproduction and Physiology Group, Animal Research and Development, Agricultural Products Division.